Haemolysis and coagulation

[Cheman]

My text book says that thromboplastin which is produced by damaged tissues acts as the catalyst to convert prothrombin into thrombin. However, I have seen on the internet references to a Prothrombin activator being the catalyst and that this results from thromboplastin and other factors. Which is true? What really does happen?
Thanks.

[iansmith]

Coagulatuion may begin from any of the coagulation factors from different pathway depending on the extent of damage and time of the signalling. Both the test book and the internet references are more or less rigth. http://www.biocarta.com/pathfiles/h_intrinsicPathway.asp

thromboplastin: an enzyme liberated from blood platelets that converts prothrombin into thrombin as blood starts to clot

prothrombin - a protein in blood plasma that is the inactive precursor of thrombin

http://www.thefreedictionary.com/coagulation%20factor

[Cheman]

So, which is it which converts prothrombin to thrombin? Thromboplastin or prothrombin activator? Thanks.

[Cheman]

Also, apparently platelet factors are released when platelets lyse or burst. hy do they burst?

[iansmith]

So, which is it which converts prothrombin to thrombin? Thromboplastin or prothrombin activator?

Both compound convert prothrombin but using different pathways.

http://www.labtestsonline.org/images/coag_cascade.pdf

apparently platelet factors are released when platelets lyse or burst. hy do they burst?

Again different pathways comes into play but briefly you have antibodies, complement and bacterial factors.

[Cheman]

Why do they burst?
Also, what causes the reflex of vascoconstriction when we are cut?

[Monique]

Platelets release their granula upon activation, they don't actually burst. The vascoconstriction is mediated by factors released by the damaged tissue and the activated platelets.